Sister & Brother Complex
by exotic-cheesecake
Summary: Ah, puberty. Makes boys grow muscular and makes girls curvy and shapely. A change Len didn't expect to see from his twin at all. And this change is waking feelings within himself he didn't realize before. (read and review? )
1. Len's Observations

**Author's Note:** Hello all :) This is more of a disclaimer. I am rusty to writing, and I will be practicing again and posting more stuff. My _Gotcha!_ got a lot of good views and some nice reviews. So I'm thinkin maybe I should post some more dirty stuff with our favorite twins, but w/ plot eh? So that means chapters. & yes, that means no good bits in the first chapters haha! Anyways, enjoy the read yeah?

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Rin Kagamine was maturing, and Len did not like it.

He watched the process happen slowly. He was always amazed how the female transformation construed. His cute little sister who played with stuffed animals and watched dumb cartoons with, is now wearing shorter skirts than usual, and putting her hair up in weird hairstyles he's never seen, and worse of all, the makeup.

But the most noticeable change was her body. Their bodies used to be similar, Len and Rin. They both had long, slender bodies with petite limbs. They looked so identical they'd switch clothes and pretend to be each other. But that was in the past.. Now. Well, femininity had finally approached Rin with kindness. Rin's straight, rectangular figure… well, fleshed out and she began to have more of a curvature body. Len first noticed when they were snuggled on the couch, and she hugged him tight. He felt her bosom press against him… and that was the thing. She HAD a bosom. Not her flat chest.

Len just didn't like it. And he surely didn't like how it made him feel towards her.

It was early in the morning, and Len had just finished getting dressed and was coming downstairs for breakfast. What met his eyes was shocking. His twin was sitting at the table with the makeup of a model, painted nails, and braided hair. She played with the school uniform; she added belts and wore bright colored knee-highs with wedges, lowered the top so that she showed a bit of cleavage. She looked much, much older than she was, merely 16.

Len glowered at her and set his bag down on the table. She looked up at him, her brows furrowed. "What?"

He visibly looked her up and down and gestured towards her outfit with an open palm. "What the hell is this?"

Rin looked down at her outfit and stuck out her chest a bit. "My clothes? Don't I look super cute?" She giggled as she stuck a piece of toast in her mouth.

"Y-you," Len stammered, unable to find the right words. He looked at her and pierced his lips. He had to stop himself from looking at the line of her chest that peeked out of her top. "You can't go like that."

She looked at him with a raised brow, and swallowed. "Why not?"

"You just can't. I won't allow it." Why didn't she understand? If she went to school like that, and knowing how the guys are at their school, she'd surely have a LOT of unwanted attention. And that is exactly what Len was afraid of.

"Excuse me? I can wear whatever I want. You don't control me, okay? Leave me alone." With that, Rin hopped up from the table and exited the door, her bag slung over her shoulder. Len went after her, and they walked to school, with Len at a distance.

Len's fears were definitely confirmed. Boys ogled at his sister and nudged their friends to look as his sister walked the halls in her short uniform skirt and revealed her shapely legs. It was like she was completely oblivious with how low her top went when she bent over, or how her yellow striped panties were visible if she bent over far enough. Len made sure to shoot the male students a glare before they could even think about looking at her. As for Rin, she didn't really notice the attention except from her friends, who showered her with compliments with how good she looked.

 _Encouragement she does not need_ , Len thought bitterly.

Unfortunately Len couldn't be glued to his twins side forever, and had to part from her so he could go to his Chemistry class. He struggled to focus to the teachers lecture however, too distracted by mental battles going on his head.

Why was he feeling so… protective towards Rin now? Was protective the right word? Maybe not. He buried his face in his palms and exhaled. Usually he didn't care what she wore, because she was a petite, annoying little brat who bugged him a lot and wore her bow on top of her head like always. She was never 'sexy' or 'womanly' in his eyes. And now, well now, she's quite different. _Voluptuous_. A word Len would have never associated with his twin.

Next thing Len knew it was nearing the end of the day, and he was exhausted from trying to be Rin's fuckboy shield, and was going to meet up with his twin at the gate so they could walk home. He was walking with Kaito, his best friend. They talked about finals, and other regular topics until Kaito stopped and cleared his throat.

"You know, about your sister…" Kaito started, a frown spreading on his lips.

"...What about my sister?" Len scowled at the blue-haired boy. Kaito knows that they had an unspoken code about him speaking with Rin, they were best friends. Don't date each others sisters. He would kill Kaito.

"Well, lets say she… has an admirer. Whom she happens to admire back," and as they both were nearing the gate, Kaito stepped in front of Len to prevent him from going further. "A lot."

"Kaito, what the hell?"

Kaito clasped his hands together pleadingly. "Don't get mad, okay? Just breathe and think about how your sister is mature now and-"

Len moved Kaito out of the way, and what he saw at the gate yards away stopped him in his tracks. His cerulean eyes widened.

Rin was with a male student, clearly a senior, with a deep purple ponytail and a stupid smirk on his face. He had his hands on her hips and pressed her against him. His twin was dumbstruck in infatuation, and was giggling and blushing at his exploring hands.

Only one senior had that stupid eggplant color of hair. Gakupo.


	2. Intentions and Misunderstandings

**Author's Note** : Um. Hello! So... after almost literally a year. I have discovered my lost rin/len fanfic here and have decided, at 1am to type out a second chapter. Trying to get better of course. I really hope you enjoy. Read and leave a comment. Enjoy Chapter 2 of Brother & Sister Complex: Intentions and Misunderstandings

* * *

"I'm a woman." Rin told herself earlier that morning, as she circled in the mirror. She had nodded in approval at her reflection, and gave a cheeky smile. She was happy that she had style that rivaled the oh-so-sexy Miku Hatsune that everyone at school drooled over. This year was going to be different for sure.

And as she expected, she got a lot of praise from her friends at school, and lots of surprised or lingering looks. Rin was screaming on the inside. She was definitely going to get a boyfriend this year! No longer will she be known as the "10-year-old wooden plank."

Even though she was feeling super excited, her twin was like a hawk the entire day. Glancing over his shoulder at lunch at her, making sure she was okay. Walked a little too closely in the hallways when he could. It frustrated Rin. When was Len going to learn that she is a woman now? She can take care of herself. She knew Len was always there for her, to protect her, to be at her side always. But things were going to be different from now on. No more Len taking care of baby, crying Rin.

After a long day of tedious first-day etiquette at school, Gumi and she walked out of the building, talking about the boys that were cute in their classes and regular schoolgirl jargon. Gumi nudged Rin at the side, interrupting her.

"What is it?" She asked, and she followed Gumi's gaze to the front gate of the building. Her mouth popped open.

"Oh. My. Gosh."

It was Gakupo, possibly the hottest guy in the entire class, or in the entire school. He leaned against the stone edifice by the gates, talking to a group of friends. He casually twirled strands of his long purple hair around his fingers as he talked, and his blue eyes danced as he laughed .Does he purposely try to look gorgeous with everything he does? Or was it just natural?

And as if it were a movie, his ice blue eyes glanced up and met her cerulean ones and the gaze was held for a solid four seconds. She blushed immensely and looked around to make sure it was her he was gazing at

He visibly chuckled and gestured with his head, a ' _come-here_ ' notion.

"Rin he's looking at you!" Gumi gushed. "He's gesturing at you. Go over there!"

Rin was pushed forward by her ever-so-helpful best friend into Gakupo's group of friends. They regarded her with laughter and jokes, easily accepted. Rin didn't know what to say exactly - does she act cool and suave, as if his very acknowledgment of her didn't matter when it clearly did?

 _Oh gosh. He is like a prince. A handsome purple-haired prince that I want to kiss and-_

"The summer treated you well, I see." Gakupo said with a grin on his face, his eyes drifting up and down her body.

Her cheeks reddened even more. "Oh. Um, thanks. I do a lot of… exercise...sometimes."

 _Really, Rin?! Come on. You "do a lot of exercise sometimes"? You couldn't say something that doesn't sound awkward?!_ She berated herself in her mind before his laugh interrupted her thoughts.

"I do a lot of exercise too. We should work out together sometime. Get sweaty." He said cheekily. But Rin, in her innocence and naivete, didn't catch the double meaning.

"Oh totally! I know this really cool gym near my house that I had been going to, it's not exactly like 'high-class' but-"

"I see you toned your arms.." Gakupo interjected, placing a palm on her forearm, his fingertips tracing back and forth. The feeling made Rin get butterflies in her stomach. She giggled and her face was a deep red now.

Rin showed him different muscle groups that she worked on over the summer, and he was glad to feel and be impressed on how strong her body actually was. From a distance, it looked like he was feeling her up, but really she was proudly showing herself off.

Before she could say anything else, a blur of blonde appeared in front of her, arms stretched out over her person. And accompanying him at a distance was Kaito, her twin brother's best friend since childhood.

"What the _hell_ are you doing to my sister, you purpled-haired fuck?" Her twin brother yelled at her purple prince. He never sounded so angry before. So… threatening. It surprised her. However the surprise was soon replaced by embarrassment.

She scowled at the back of his head. "Len! What do you think you're doing?!"

"Yeah, _Len_. What do you think you're doing? We were just talking." Gakupo said nonchalantly, his hands raised in mock defense.

"You put YOUR hands on Rin. You don't think I know what your motives are, you pervert!? I will end your life if you do that again."

"I think you're just misunderstanding-"

Len grabbed a fistful of Gakupo's uniform shirt and brought him down to his height. "NO. You're misunderstanding. Let me be clear. Touch her again, and you will regret ever crossing paths with me."

Gakupo disregarded Len's stance and threats and looked over him at her. "Hey, Rin. I didn't realize your brother was actually your boyfriend. Hit me up when he loses the sister complex."

And with that, her purple prince released Len's grip and turned away.

Len turned to her, and gently clasped her arms. "Are you okay? Did he say anything weird to you?"

Rin had her eyes downcast as her twin hounded her with countless questions, his voice white noise in the background of her thoughts. Why? The first time she ever gets noticed by a guy, the first time someone looks at her with those expressions… and she loses it. No. Len takes it away from her.

She shook from his grasp aggressively. "Leave me alone! You ruin everything. Why can't you let me be happy for once without interfering?" Tears started to form in her eyes, making her cerulean color sharper than ever.

His brother's worried expression softened to sadness. "Rin. I already know that guy wasn't going to make you happy! He just wanted-"

"How do you know that!? Are you a psychic? Do you read minds? Just don't talk to me."

Rin stormed off before the tears hit her cheeks, leaving a bewildered and confused Len behind.


	3. Len's Feelings

**WARNING: GRAPHIC LANGUAGE AND SCENE IN THIS CHAPTER.**

 **Author's Note** : Hello all! Yes, about another year later a chapter is released lol. I seem to do these chapters when I'm in a writing rut but no fear! I'll try to put in chapters that are not a year apart. I'm kind of worried about this chapter because I feel like I'm not connecting Len's personality in this writing. But none the less, I hope you enjoy this chapter.

* * *

Len being confused was an... understatement.

After Rin stormed off on her way home, he was left there dumbfounded. The students that were gathered at the entrance gate departed, and it was only him and his best friend left. What had he done wrong? It was obvious that Gakupo had impure intentions! And he couldn't just sit by and watch as he groped her and touched her. Running his big hands over her thighs and arms, disgusting. He had to stop it. So why was he being punished for that?

The blonde boy shook his head and sighed.

Kaito placed a hand on his distressed friend's shoulder, "You know, Len, maybe it's time to stop being so overprotective... She's almost an adult. She can take care of herself."

Len offered a glare and shoved his hand off. "It's not my fault she doesn't see that Gakupo is a sleezy douchebag. Who else is supposed to watch and prevent things like this?"

"Yeah, but like Gakupo said, you're kind of acting like a..."

"A what?"

Kaito pursed his lips together and exhaled. "A jealous boyfriend."

Len's eyes widened in surprise. "What? Am not."

Kaito gave Len a long look before shaking his head. "You're oblivious. I'm going home. Text me later."

And with that Kaito left.

"What the hell..."

*

Some time later after Len arrived at home, he was greeted with his foster sister, Meiko, with dinner. She had an almost empty wine bottle on the counter, and was humming along to some song he didn't know while she was finishing dinner.

Meiko was more like a mother than a sister to him and Rin. She was really a distant relative of the family and took them in when their parents had traveled for work. She worked as a secretary to some big corporate heir downtown, and made decent money to take care of them. Now they just choose to live with her, with their parent's blessing.

"Hey, Meiko. Where's Rin?"

Meiko grinned. "Len. Your sister's upstairs in her room."

"Ah."

He slumped on the counter and cupped his cheek in his hand. Meiko saw this and did the same pose in front of him, with a knowing expression on her face.

"What's wrong Lenny, Len, Leeeeeennn?"

She was drunk, like the majority of the time. And when Meiko was drunk, she was very silly.

"Ah, nothing. Just..." He stopped, not really wanting to go further.

Meiko perked up and rested both of her hands on her face, looking very interested. She had a cheesy smile on her face. "Tell me aaalll about it Len. Tell me what troubles you."

Len pondered on it for a moment. Meiko usually didn't remember much when she was drunk, so he thought ' _Why not?'_ He needed to get this off his chest.

"Meiko, wouldn't you do anything to protect us? Like, if you saw me with a girl you didn't like and didn't think was good for me, wouldn't you try to intervene to make sure I didn't get hurt?"

Meiko's brown eyes went to the ceiling in thought. After a few seconds they met his. "Well, I really wouldn't have a say about what girl you have relations with Len. That's your business. You're old enough to make your own decisions with that, I think."

Len frowned. Why was she sounding so sane in her drunken stupor? Was he really being overprotective?

Meiko smirked a little and poked his nose. "Why? Is there a girl you're interested in trying to get with someone?"

The question made his heart jump. "W-what? No. Hell no. No way."

It's _Rin_ , for crying out loud.

"You're cute, Len. There will be other girls who will fall for your pretty boy act," Meiko said teasingly, pulling herself away from the counter. "Dinner is on the stove. I'm heading upstairs to bed. Don't make that expression too long, you'll get wrinkles and ruin that pretty face."

She ascended the stairs and left him alone in the kitchen with his thoughts.

Interested? That's crazy. Sure, he's been feeling weird about her recently, but who wouldn't when your sister turns from a crying, whiny baby that needed you every five seconds to a... "woman" who wanted to throw herself onto any guy?!

Len got his dinner, Meiko's notorious spaghetti, and finished before he drug himself upstairs to his room. As he was about to enter his room, he remembered that he left his boxers in the bathroom from this morning.

He twisted the doorknob and entered without a second thought, and was greeted with a shrill scream.

"Len!? Get the hell out!"

The first thing that met his sight was Rin in the bath, her legs out on the edges of the tub and her smartphone in her right hand. He didn't know how to react. He was so bewildered and couldn't look away for a few seconds, but was then was met with a loofah to the face. It was then he snapped back to reality and exited the bathroom as swiftly as he could.

 _W-what just happened?!  
_

Len escaped to his bedroom and covered his beet red face with his hands. The image of her was burned into the back of his eyelids and he couldn't stop thinking about what he saw.

The water droplets cascading down her neck and in between her breasts, her slender legs perched on the tub-

 _Stop! Stop it. You can't think of her like that you can't…_

He felt a throbbing in his pants.

"What is wrong with me..." He said out loud, closing his eyes tightly.

Len decided to distract himself. He couldn't be alone with his thoughts anymore. Plopping himself on his bed, he pulled out his smartphone and saw that he had a message from Kaito.

[kaito]: hey dude ^_^ feeling ok?

 _Ugh, Kaito. Picking the worst times to text me. I am not doing okay at all._

He chose to ignore it and pulled up his browser. _Regular porn should be good enough, right?_

He searched for a video from one of the genres that he usually liked watching, particularly one called 'girl gets creampied twice" He started to stroke himself through his pants as he watched a video of a girl getting rammed from behind. She had huge tits, and a big ass. Something all guys liked.

Len's breath started to become labored as he matched his strokes with the guy's in the video. Closing his eyes, he imagined himself inside the girl in the video, and that her moans were from him fucking her. He pulled his cock out of his sweatpants and teased himself some; using a finger to trace along his member and in response it twitched a little. He then gripped tight and stroked furiously, dropping the smartphone on his chest as he did so. He felt himself about to climax, the girl's moans in his ears, and right before he did an image popped in his mind.

 _Rin in the bath.  
_

The pressure started to build, and his strokes became erratic. He felt it coming.

"Ahh.." He gasped and with a few pumps into his hand, Len came onto his chiseled stomach. After a few minutes of gathering himself, Len stared at the ceiling.

 _This is not good._


	4. Purple-Haired Prince

**Author's Note : **Hi hi~ See, I told you. Another chapter within the week. I'm doin' pretty good aren't I? c: and it's a bit longer! what do you guys think of my writing style? leave a comment! **  
**

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"Stupid, stupid, stupid, stupid!" Rin grumbled to herself as she power-walked to her house. Her hands were gripped tight into fists, and she ground her teeth together in anger. Even as furious as she was, tears managed to form in the corners of her eyes, one cascading down a part of her left cheek. Shaking her head, she wiped them away with her forearm. She couldn't allow herself to cry anymore. She's not that weak little girl that everyone used to know. And she refused to go back to those days of clinging onto someone and hiding.

Rin was definitely going to workout tonight and imagine the air as Len's face and swing at it until her arms are dead weight. Why couldn't he get it? She was a woman now. _Practically_ an adult. If she wanted to talk to guys, she could. If she wanted to change her style, she could. It irritated her how much he was acting like her parent. Complaining about her clothes, what guy she talks to… she's sick of it!

Rin eventually neared the house and opened the front door quite abruptly, still frustrated within her thoughts. But it was so abrupt that Meiko jumped and tipped over her wine bottle on the kitchen counter, spilling almost over half of it on the floor. "Shit!"

"Ah, sorry Meiko! I didn't mean to scare you." She assisted her foster sister in cleaning up the mess with paper towels. During this Meiko noticed the teary-eyed Rin through her peripheral vision.

After throwing the wine-soaked paper towels away in the trash, Meiko put a hand on the young teen's shoulder. "Rin? Are you okay? Where's Len?"

It seemed this was the thing that broke the dam in Rin's mind that were holding back the tears. She collapsed into her arms and sobbed into her bosom. "I'm never getting a boyfriend! Len ruins everything."

Rin told Meiko (a lot of it sounded unclear because of her gasps and sobs) the events that happened prior, and she listened intently with an occasional nod or shake of the head. A wide range of emotions spanned the blonde girl's face: a smile from recalling events with Gakupo, furrowed brows and anger discussing the incident that occurred between her twin brother and him, and then sadness from her lost chance of love. After a few moments of silence, Meiko cupped Rin's face in her hands and gave a soft smile.

"Rin, you know how your brother is. He's used to always being your protector. It'll take him some time to realize you're not a little girl anymore, " As she spoke she wiped away a tear with her thumb, "He just cares about you. Let him know how you feel, and maybe he'll get it. And besides, you're a knockout. You will definitely win over a boy's heart soon so don't even worry about that."

Rin's heart warmed at her words and she gave her a hug. "You always know what to say, Mei. Thank you."

"Of course. Now go upstairs and channel your emotions through a workout."

Rin nodded with a grin and ascended the stairs to her room. Gakupo didn't know this, but she possibly, _may_ have lied about going to the gym near her house. She knew that the membership there was way too expensive for Meiko to cover monthly, so she decided to do some home workouts during the summer to get rid of tummy fat. And she hadn't stopped since.

Thoughts of Gakupo fueled her energy as she did her cardio in her room. Was this the act of falling in love? Everything that she did, he was always on her mind. The way he laughed, smiled and looked at her made her feel… _excited?_ Was that the right word? When he trailed his slender fingers down her arm at the gate, her heart felt like it was going to jump out of her chest. Rin wanted him to touch her more, all over.

Rin stopped in the middle of her jumping jacks and put her hands on her knees to catch her breath.

 _What was that thought? I want him to… touch me more?_

A ' _bing!_ ' tone erupted from her phone on her bed.

She wiped the sweat from her palms on her shorts before checking her phone. It was a message from an unknown number:

 **[+82)10-894-XXXX]: hey girl**

Rin furrowed her brows together and her fingers tapped on the screen.

 **[Rin:]: who is this ? -_-**

As she waited for the stranger to reply she gathered some clothes and other necessities for a shower. Entering the bathroom, Rin set her clothes on the counter and began to strip off her sweaty workout garments. She decided against a shower and began to draw a hot bath before her phone emanated another ' _bing!_ '.

She opened her messages and her heart skipped a beat.

 **[+82)10-894-XXXX]: its me gakupo. gumi gave me ur number.  
is that ok? Or is ur bro going to freak out again lol**

Rin stared at his message, not really sure how to respond. Come to think of it, she's never texted a boy before. Well, not a boy that she liked anyway. After a few minutes of thought she replied.

 **[Rin]: oh hi! _ im sry about my twin. It wont happen again. wats up?**

 _Yes, good. Sound casual Rin_.

She slipped into the bath, carefully holding her smartphone above the water. Normally the person she was texting would have to wait until after she was finished, but this person wasn't just any other ordinary person. This was her purple-haired prince and he hadn't given up on her yet! She stared at their conversation intently before he saw another message pop up.

 **[3Gakupo3]: nm just thinkin about u ;) wbu**

Rin hid her face from the nose down beneath the water. She couldn't tell if her cheeks were hot from the bath or from him. She couldn't stop staring at his words. He was thinking about her? Does he like her too? This had to be a dream come true.

 **[Rin]: just relaxing in the bath rn~! ^_^ had a great workout session  
so im soothing the muscles**

 _Bing!_

 ** _[3Gakupo3]: oh really_ _.._ _pr_** _ **ove it  
**  
_

Rin nearly dropped her phone in the bath.

 _Prove it…? Like, take a picture?_

Rin's heard of girls at school that take pictures for their boyfriends, in lingerie or cute outfits to make them happy. She could do that, right? Gakupo messaged her first, and he was thinking about her… he's completely interested. But does she want to completely expose herself to him like this? Through text? But would she ever get another chance like this with him? Rin couldn't risk that.

She pulled up the camera app and positioned the frame over her body. She made sure she covered her breasts with her arm and she tried to make the cutest kissy face possible. Rin snapped the picture and observed it. Technically she wasn't showing anything, just her face and part of her chest. Harmless.

Her thumb hovered over the SEND button.

She pressed it and shut her eyes tight. A couple of minutes passed until she heard another,

 _Bing!_

 **[3Gakupo3]: wow ur so cute~~. could u maybe show me more ?**

Rin's heart was slamming against her chest.

"M-more?" She whispered, her cerulean eyes wide in surprise. Some time passed while she debated with this, until she heard another _bing!_ from her phone.

 **[3Gakupo:3] if not its ok. tht was probably weird to ask sry**

Rin bit her lip. She was nervous; Rin never exposed herself to anyone like this before. But he seemed really sincere. Her fingers went away at her screen:

 **[Rin]: no its ok. just a sec~ (^-^)**

Once again with the camera app she angled her phone farther up above her body. Just as she was adjusting herself she heard the doorknob and rattle and her heart jumped in her throat.

Len had strolled into the bathroom without knocking, and Rin was frozen in shock. They stared at each other for what seemed like ages before she snapped back into reality and screamed. Her phone fell to the tile floor besides the tub and her hands flew to her chest and between her legs.

"Len?! Get the hell out!"

After a moment's pause, the boy ran out and slammed the door behind him, leaving her with the shock of her life. Her twin just witnessed her taking naked pictures of herself.

Naked.

Her.

She wanted to _die_.

* * *

 **Author's End Comments** : Oh gosh guys. We've all had that fuckboy trying to ask for nudes, amirite? leave a suggestion for what gakupo's next text should be! XD that should be funny


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